LEGAL CHALLENGE OF THE UNGAGED WATERSHED1

The lack of uniform techniques for estimating design discharges in ungaged areas is a source of growing concern in the courts now faced with challenges to floodplain boundaries and culvert design for highway crossings. This paper summarizes a court case in which calculations of the design discharge and the hydraulic backwater effects of a major highway culvert were contested by the plaintiff. Emphasis in the paper is placed on the variation in computed flows and the interpretation of the court in the face of diverse hydrologic methods for the ungaged watershed. The results of a preliminary evaluation of ungaged watershed methods applicable to Pennsylvania are also reported in terms of standard error and bias.     

FLOOD EVENT MODELING - A STUDY OF TWO METHODS1

: Despite the advances in catchment modeling in recent years, engineers still face major problems in estimating flood flows. Application of unit hydrograph and runoff routing models to five United Kingdom catchments shows that either can be tuned to predict, on a test event, the routing effects of a catchment with equal accuracy. The larger remaining problem is the prediction of losses from rainfall and this study shows how alternative ways of describing the within event distribution of these losses can be an important factor controlling the success of the overall model. Other problems include the risks of extrapolation to larger events, baseflow separation methods, rainfall patterns, and inevitable errors in the data.     

DUAL PURPOSE DETENTION BASINS IN STORM WATER MANAGEMENT1

Storm water management contributes to flood hazard mitigation; but new approaches now being developed consider also the reduction in particulate pollution and stream erosion. Such approaches involve retardation of storm runoff, or detention programs of some kind, and detention basins are usually required if large storms are to be controlled. The usual concept is that future storms occurring after development should have no more adverse effect than similar storms would have had before development; but a number of different criteria are being used. If control of storms of different sizes is required, only a small amount of additional capacity is required to obtain retention of particulate pollution in the same basin. In at least three different parts of the country, such dual purpose detention basins are being required of developers. In such programs the developers bear the cost, the governmental contributions are not involved.     

THE USE OF FLOOD POTENTIAL INDICES FOR FLOOD PEAK ESTIMATION ON UNGAGED WATERSHEDS1

: The construction of a flood peak index map was attempted for use by hydrologists in the simple format of rainfall maps. Since flood peaks are highly dependent on watershed area, the effect of area was removed. By regression analysis flood peaks of 2.33 and 100-year return periods were found to be proportional to watershed area to the 0.8 and 0.7 powers, respectively. Therefore, indices C_{2 33}= Q_{2 33}/_A0.7 were completed at each gage and plotted on a Pennsylvania map. It was attempted to further remove some of the scatter by regression of C with several other watershed parameters like slope, percent forest cover, and watershed shape, but no significant correlation could be found. The index maps, drawn without attenuation of the scatter, can be used by hydrologists to compute flood peaks as Q = CAⁿ (with n = 0.8 and 0.7 for the 2.33 and 100-year flood peaks, respectively). Flood peak safety factors can be based on visual observation of the index variation in the vicinity of the location for which the flood peak estimate is needed.     

A PLANNING METHOD FOR EVALUATING DOWNSTREAM EFFECTS OF DETENTION BASINS1

While storm water detention basins are widely used for controlling increases in peak discharges that result from urbanization, recent research has indicated that under certain circumstances detention storage can actually cause increases in peak discharge rates. Because of the potential for detrimental downstream effects, storm water management policies often require downstream effects to be evaluated. Such evaluation requires the design engineer to collect additional topographic and land use data and make costly hydrologic analyses. Thus, a method, which is easy to apply and which would indicate whether or not a detailed hydrologic analysis of downstream impacts is necessary, should decrease the average cost of storm water management designs. A planning method that does not require either a large data base or a computer is presented. The time co-ordinates of runoff hydrographs are estimated using the time-of-concentration and the SCS runoff curve number; the discharge coordinates are estimated using a simple peak discharge equation. While the planning method does not require a detailed design of the detention basin, it does provide a reasonably accurate procedure for evaluating whether or not the installation of a detention basin will cause adverse downstream flooding.     

Reconstructed Stream Flow for the Salt and Verde Rivers From Tree-Ring Data1

ABSTRACT: The Salt and Verde Rivers of central Arizona provide the water supply for metropolitan Phoenix and a considerable acreage of irrigated agriculture. Rapid urbanization has caused concern over future water supply and aggravated flooding in the already flood-prone Salt River Valley. Tree-ring data were used as a proxy source to extend the annual and seasonal runoff records back to A.D. 1580 and thus to determine whether the period of record for annual discharge adequately represents the long term flow characteristics of the two rivers. Results show that several periods of extended low flow have occurred during the past 400 years, many of which were more severe then any comparable period since 1890. The low flow periods appear to have a recurrence interval of about 22 years. Also the gaged records contain an above average number of high seasonal and annual flows when compared to the entire 400 years. The reconstructions contain important implications for future water supply and flood potentials in the Salt River Valley.     

ANALYZING URBANIZATION IMPACTS ON PENNSYLVANIA FLOOD PEAKS1

ABSTRACT: The impact of man made change on the hydrology of developing watersheds is frequently measured in terms of the ratio: flood peak after development to flood peak before development over a range of return periods. However, the analysis of urbanization effects on flood frequency presents a vexing problem because of a general lack of flood data in urban areas and also because of nonstationarity in the development process. Clearly, the flood peak ratio depends on the impervious fraction and percent of basin sewered and these factors have been taken into account in recent urban flood peak models. In genral, these models are developed either by: (1) split sample analysis of available annual flood data, or (2) by computer simulation using mathematical watershed models capable of representing man made changes. The present paper discusses the results of work in progress to characterize the impact of urbanization on small developing watersheds in Pennsylvania.     

洞庭湖水灾机制和减灾分析

分析了洞庭湖洪涝灾害的成因机制,指出长江三口和湖南四水的来水来沙是制约洞庭湖演变和造成湖区水灾的关键因素,应重点协调江湖关系和湖垸关系,退田还湖,平垸行洪,堵疏并重,泄蓄兼筹,并借助未来的三峡工程来改善湖区的水文环境。     

淮河流域洪涝变化可预报时间研究

在先前的淮河流域洪涝变化基本特征、混沌特征、耗散性等基础上,采用Ｋｏｌｍｏｇｏｒｏｖ熵和Ｌｙａｐｕｎｏｖ指数谱分析了淮河流域洪涝变化预报时间。研究表明,淮河流域洪涝变化长期不可预报,短期是可以预报的,其可预报时间为４￣６年,以４年为较合适。     

人工纳米材料富勒烯（C60）低剂量长期暴露对鲫鱼的氧化伤害

为更好地判断人工纳米材料(富勒烯,C60)对水生生物的潜在健康危害,以鲫鱼(Carassius auratus)幼鱼为受试生物,研究了低剂量C60(0.04～1.0 mg·L-1)长期(32 d)暴露对鲫鱼的氧化伤害.结果表明,各实验组中鲫鱼幼鱼脑、肝脏、鳃组织中的还原型谷胱甘肽(GSH)含量都发生显著降低(p＜0.05),其中1 mg·L-1 nC60,aq的暴露对鳃组织GSH含量的抑制率为14.3%,高于对鱼脑、肝脏组织中的抑制率;肝脏组织中过氧化氢酶(CAT)和超氧化物歧化酶(SOD)活性,以及鳃组织中Na -K -ATP酶活性均被显著激活,其最大活性分别是对照的121.34%(0.04 mg·L-1暴露组)、114.80%(0.04 mg·L-1暴露组)和348.59%(0.20mg·L-1暴露组).实验结果揭示,长期暴露引起机体组织的氧化应激可能是水环境中C60的致毒机制之一.